The present invention relates to a vibrating membrane fluid circulator, in particular for biological fluids.
Numerous types of pump are known both in industrial and in biomedical fields. The following can be mentioned:
reciprocating positive displacement pumps whose main elements are pistons or membranes associated with admission and delivery valves. Their main drawback lies in the cyclical aspect of their motion and in the presence of the valves;
so-called xe2x80x9cperistalticxe2x80x9d positive displacement pumps in which continuously moving wheels deform and compress a flexible tubular pump body. The compression can be damaging for certain liquids to be pumped that include sensitive elements (e.g. blood);
xe2x80x9cimpellerxe2x80x9d pumps such as centrifugal pumps based on a vaned rotor or a vortex. Their drawback lies in the high speed of rotation which generates shear in the fluid streams, friction, and cavitation, all of which phenomena can be damaging to fragile fluids; and
axial turbine pumps in which fragile fluids suffer likewise from the same drawbacks as in the preceding pumps.
Also known is a vibrating-membrane fluid propulsion device, as described in document FR-A-2 650 862. That device provides a technical solution which is not always suitable for obtaining the hydraulic performance required by most industrial and biomedical applications.
The vibrating membrane fluid circulator of the invention proposes solutions whereby the fields of application of the circulator are enlarged, the hydraulic performance thereof is improved, the circulator is more compact, and finally the pump body can be for a single use only, which is advantageous in the biomedical field.
To this end, the fluid circulator of the invention comprises an internal hydraulic circuit successively made up of an admission orifice, a pump body, and a delivery orifice, the pump body defining, in operation, a space having rigid walls between which a deformable propulsion membrane is placed. The membrane has means for coupling its end situated adjacent to the admission orifice to a drive member for generating a periodic excitation force substantially normal to its surface. Provision is also made for means to keep the membrane under tension, thereby enabling it to constitute a medium for waves travelling from the end of the membrane subjected to the excitation force towards its opposite end. Displacement of these waves is accompanied by forced damping due to the shape of the rigid walls, so that mechanical energy is transferred from the membrane to the fluid, with this appearing in the form of a pressure gradient and of a fluid flow. The characteristics of the pressure gradient and of the fluid flow are related to the dimensions of the pump body, to the dimensions of the membrane, to the shape and the spacing of the rigid walls, to the mechanical characteristics and the tension state of the membrane, and to the parameters of the excitation applied thereto.
In a preferred embodiment, the periodic excitation of the membrane is implemented at one of its natural frequencies, and in particular at its first natural frequency. The values of such natural frequencies are associated with the mechanical characteristics of the membrane and with its tension state. The excitation frequency should be kept down to low values of the order of 40 Hz to 50 Hz so as to avoid localized pressure effects and shear effects between fluid streams.
In another embodiment, the space having rigid walls is defined by two disk-shaped walls, between which there is placed a deformable membrane that is also disk-shaped. This circular architecture possesses an effect whereby energy radiating from the outside towards the center of the system is concentrated, thereby making it possible to generate pressure gradients compatible with those required by industrial and biomedical applications. This solution also makes it possible to operate with very low excitation amplitudes at the periphery, thus making it possible to avoid injuring fragile fluids. Another advantage is that it makes it possible to tension the membrane very simply since it suffices to take action solely on the outside edge thereof.
In another embodiment, the membrane is made up of an assembly of superposed membranes, with the membranes being separated by fine spacers of a material having very low stiffness. This dispositions makes it possible to increase the mass of a membrane while retaining a natural frequency close to the natural frequency of each of the membranes when identical membranes are assembled together.
In another embodiment, flexible deflectors are carried by the membrane and press against the pump body. The deflectors modify the length of the hydraulic circuit and the way in which fluid flow speeds vary in the circulation space. This disposition enables the circulator to operate in association with rigid walls that are spaced further apart, which is favorable for propelling fluids that are fragile or that are laden with particles.
In another embodiment, circular flexible lips are carried by the membrane and bear against the pump body, the lips thus providing a simple non-return valve relative to the fluid flow, thereby satisfying requirements, particularly in certain biomedical applications.
In another embodiment, the circulator pump body forms a unit that integrates the following in inseparable manner: the membrane, the admission and delivery orifices, and the walls defining the space in which the membrane is housed. These walls are rigid and are held apart from each other by spacer means. At the periphery they are connected to the membrane via flexible walls. Inside the circulation space, the membrane has perforations at said periphery, and also a central orifice, thereby enabling the fluid to flow from one side of the membrane to the other. This technical disposition makes it possible to provide a pump body whose operation is not disturbed by the value of the admission pressure.
The membrane excitation means are constituted by an electromagnetic motor whose feed circuit for receiving excitation alternating current includes a power amplifier circuit and a circuit for generating an excitation signal so as to provide the possibilities of modulating amplitude, of programming, of storage, and of generating complex excitation signals, e.g. simulating heart beats.